Fragmentation of block copolymer micelles in mixed ionic liquids

Block copolymers self-organize into a myriad of micellar nanostructures when placed in selective solvents, offering great potential as drug delivery carriers and nanoreactors. A comprehensive understanding of the dynamics of micelle formation and equilibration can be very useful to optimize structure-property relationships. Micelle fusion, fragmentation, and chain exchange present the likely relaxation mechanisms leading to micellar equilibration. The present study examines the kinetics of fragmentation of 1,2-polybutadiene-b-poly(ethylene oxide) block copolymer micelles in ionic liquids after a temperature jump. Micelles are characterized using in-situ characterization techniques such as dynamic light scattering, small-angle X-ray scattering, and transmission electron microscopy to obtain the tie evolution of average micelle size, aggregation number, and size distribution, respectively. The role of the driving force for fragmentation on the kinetics is investigated by altering the solvent quality after micelle preparation. Dilution of a selective solvent with a less selective solvent is found to influence the kinetics of fragmentation.